Technical Field
Described herein is a process for manufacturing semiconductor devices of a surface-mount type, in particular of the Quad-Flat No-Leads Multi-Row (QFN_mr) type, comprising providing a metal leadframe, in particular a copper leadframe, which includes a plurality of pads, each of which is designed to receive the body of the device, said pads being separated from adjacent pads by one or more rows of wire-bonding contacting areas, the outermost rows from among said one or more rows of wire-bonding contacting areas identifying, together with outermost rows corresponding to the adjacent pads, separation regions.
Various embodiments may be applied to QFN_mr devices for applications of power control, radiofrequency transmissions, digital conversion of physical/electrical inputs in the consumer, automotive, and industrial sectors.
Description of the Related Art
As is known, semiconductor devices, such as, for example, integrated circuits and MEMS devices, are encapsulated within corresponding packages, which perform functions of protection from and interfacing with the outside world. For instance, so-called “surface-mount” packages are known, which enable surface mounting on a printed circuit board (PCB).
In greater detail, surface-mount packages comprise, for example, the so-called packages of a “No-Lead Quad-Flat” (QFN) type, known also as “Micro-Leadframe” (MLF) packages or “Small-Outline No-leads” (SON) packages.
In general, with reference, for example, to a package of a QFN type, it comprises a resin region, encapsulated in which is a leadframe, which in turn forms at least one array of terminals that give out onto a bottom surface of the package. An example of process for producing a package comprising a leadframe is described in U.S. Patent Pub. No. US 2005/0116321.
As compared to a standard QFN device, the QFN_mr device starts from a pitch of 0.4 mm and, given the same area, has a higher number of inputs/outputs, these possibly being arranged on the bottom surface of the QFN_mr device starting from the central area occupied by the dissipater of the device, as far as its edge, whereas in the standard QFN device the inputs/outputs may be arranged only along the edges.
In standard QFN devices, the surface of the outer contacts reaches the edge of the device since there do not exist problems of detachment of the contacts themselves during singulation of the devices in so far as the contacts are supported by the structure of the leadframe. In QFN_mr devices, the contacts, before the operation of singulation is carried out, are completely insulated and supported merely by the packaging resin and by the wires; consequently, they are unable to withstand the stress transmitted by the cutting blade without delaminating. For this purpose, the leadframe of QFN_mr devices is designed so as to leave a space between the contacts and the edge of the packaging, typically of 0.1 mm.
In some circumstances, for example in the automotive sector, in order to provide the qualitative levels of the operation of soldering of QFN_mr devices on the PCB, it is a specification for the outer contacts (namely, the ones subjected to most stress from the thermo-mechanical standpoint considering the distance from the neutral point of the soldered device corresponding to the center of the device itself) to be visually inspectable in order to check that the dimensions and shape of the soldered bead respect the minimum specifications.
As regards to standard QFN devices, this specification is met by introducing a process of plating or else deposition of tin on the exposed side of the contact so as to obtain a surface set at 90° with respect to the soldering pad on the PCB, a surface that enables a soldering meniscus to be obtained that is stronger and more easily inspectable via automatic inspection.
As regards QFN_mr devices, this is not possible since the contact does not extend to the edge of the packaging.